An efficient way of providing very high sample rates, rates that cannot be provided by a single Analog-to-Digital Converter (ADC), is to use a parallel connection of slower ADCs operating in a time-interleaved fashion. An M-channel time-interleaved ADC (MCTIADC) comprises of M ADCs, each operating at a sample rate that is 1/M of the overall system sample rate. In the absence of any impairments or mismatch errors between the ADCs, i.e., assuming all the ADCs are either ideal or have exactly the same characteristics, the output samples appear at equally spaced intervals in a manner that creates a seamless image of a single ADC operating at the system sample frequency.
In practice, however, there are component mismatches between the different ADCs that severely degrade the performance of the MCTIADC system. The commonly occurring mismatches are offset, gain and uniform sample instants. In other words, the offsets and gains of all the ADCs are not the same and the ADCs do not sample at uniform sample instants of the system sample frequency. These mismatches give rise to unnecessary frequency tones or spurs in the spectrum of the signal that significantly reduce the performance of the MCTIADC system. A typical variation of Signal-to-Noise ratio (SNR) is shown in FIG. 1 wherein a tone is swept from a low frequency to almost half the sample rate of the MCTIADC system for various mismatch errors. As can be seen from the figure, the performance of the four-channel ADC is severely hampered due to these errors. Hence, it becomes imperative to estimate and correct these errors to improve the performance of the MCTIADC system.
Herein are shown techniques to minimize the effects of offset, gain and sample-time mismatches by appropriately estimating and correcting these errors in an adaptive manner. In addition, also shown is that the adaptive method can be used in a blind mode wherein the use of any particular calibration signal is circumvented. In other words, the input signal itself serves as the calibrating signal to estimate and correct the mismatch errors.